Heretofore, a fuel cell system including a fuel cell for receiving the supply of a reactant gas (a fuel gas and an oxidizing gas) to generate electricity has been suggested and put to practical use. At present, there has been suggested a technology in which a low-efficiency operation (an operation in a state of a power generation efficiency lower than that of a normal operation) of the fuel cell is performed to convert the energy of the supplied reactant gas into more thermal energy, thereby raising the temperature of the fuel cell.
The low-efficiency operation of the fuel cell is frequently performed “during starting” or “during stopping” of the fuel cell for a purpose of warming up the fuel cell under a low-temperature environment. Moreover, in recent years, there has been disclosed a technical concept that the low-efficiency operation is performed even when the temperature of the fuel cell is lower than a predetermined temperature “during the normal operation” (e.g., see Japanese Patent Application Laid-Open No. 2006-73501).